package com.xiaotu.singleton.type6;

/**
 * @author 张晓
 * @create 2020-06-18 16:21
 */
public class SingletonTest06 {
    public static void main(String[] args) {
        //测试
        System.out.println("双重检查");
        Singleton instance = Singleton.getInstance();
        Singleton instance2 = Singleton.getInstance();
        System.out.println(instance == instance2);

        System.out.println("instance.hashCode()=" + instance.hashCode());
        System.out.println("instance2.hashCode()=" + instance2.hashCode());
    }
}

//懒汉式（线程安全，同步方法）
class Singleton {

    private static volatile Singleton instance;

    private Singleton(){};

    //提供一个静态的公有的方法，加入双重检查代码，解决线程安全问题，同时解决懒加载问题，同时保证了效率
    //推荐使用
    //既懒汉式
    public static Singleton getInstance(){
        if (instance == null) {
            synchronized (Singleton.class){
                if (instance == null) {
                    instance = new Singleton();
                }
            }
        }
        return instance;
    }

}
